US patent application publication 2013/0118733 suggests the release of balls that are capable of measuring and recording information into drilling fluid, and subsequently capturing and downloading the captured data from the balls. Properties of interest are listed as temperature, pressure, density, viscosity, compressibility, acoustic property, magnetic property, chemical composition and material characteristics of the formation, fluid in the formation, drill string components, and drilling fluid. The data is said to be potentially useful for detection of corrosion, scaling, asphaltenes and waxes. The property of interest can be an ambient condition experienced by the sensor, or a characteristic of a downhole material such as the formation or formation fluid. Data can be stored within the ball, and then downloaded wirelessly at the surface after the balls are recovered from the drilling fluids. The balls can pass through drill bits and measure conditions as drilling is continuing.
Hydraulic fracturing is used to increase the area of a formation that is in communication with a wellbore and therefore increasing either production of fluids from the wellbore, or increasing the amount of fluids that may be injected into the formation from the wellbore. Hydraulic fracturing has been in commercial use for many decades, but gradual improvements in the size of fractures that can be created and the cost effectiveness of the fractures, along with developments like improved horizontal drilling, have resulted in hydraulic fracturing enabling production of hydrocarbons from formations such as source rocks or other very low permeability formations, that were previously not thought to be economically producible.
Typically, gas and/or oil, referred to as light tight oil, is produced from low permeability formations such as source rocks, by providing horizontal wells in the formations for distances of a mile or more. The formation is then fractured from the wellbores in as many as twenty or thirty places, with the fractures placed every 50 to 150 meters along the horizontal wellbore. The fractures are provided by pumping fracturing fluids into an isolated section of the wellbore that is in communication with formation at pressures that exceeds a rupture strength of the reservoir rock. The fracturing fluids are pumped to further propagate the fracture while a proppant is added to the fracturing treatment to hold the hydraulically induced fractures open when the pumping pressure is reduced.
Fractures are either propped open after they are formed by including in the fracturing fluids materials such as finely sized sands or ceramic particles, or in carbonate formations, permeability through fractures may be created by including acids in the fracturing which dissolve some minerals at the face of the fracture to create wormholes along the rock surfaces of the fractures. Proppants may be held is suspension within the fracturing fluids by including additives to increase the viscosity of the fracturing fluids, to decrease the settling rate of the proppants. Alternatively, or in addition, proppants may be utilized with lower densities to decrease the rate at which they settle in the fracture fluids,
Polymers used to increase the viscosity of fracturing fluids may be detrimental to permeability in the vicinity of the fractures, so techniques referred to as slick water fracturing have been developed. These techniques do not utilize thickening polymers, but instead rely on rapid injection of fracturing fluids.
Fracturing methods are disclosed in, for example, U.S. Pat. Nos. 8,183,179, and 7,451,820, the disclosures of which are incorporated herein by reference.
It would be desirable to be able to determine the results of a fracturing operation with respect to, for example, how many fractures were effectively opened when a cluster of fractures are created at one time, or how much fluid was entering each of the different fractures at the end of the fracturing operation as an indicator of the relative size of the different fractures. US patent application publication 2012/0193090 suggests a method by which a sensor may be placed in or just below the fluid flow path of the fracturing fluids, but the information which can be captured by this sensor is limited by the single location of the sensor.